/*
 *   Copyright 2021 zzh
 *
 *   Licensed under the Apache License, Version 2.0 (the "License");
 *   you may not use this file except in compliance with the License.
 *   You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *   Unless required by applicable law or agreed to in writing, software
 *   distributed under the License is distributed on an "AS IS" BASIS,
 *   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *   See the License for the specific language governing permissions and
 *   limitations under the License.
 *
 */

package com.aduib.boot.common.buffer;

import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;

/**
 * @description: 引用计数类
 * @author: zzh
 * @date: 2021/12/3 13:17
 */
public abstract class AbstractReferenceCounted implements ReferenceCounted {
  private static final long REFCNT_FIELD_OFFSET =
      ReferenceCountedUpdater.getUnsafeOffset(AbstractReferenceCounted.class, "refCnt");
  private static final AtomicIntegerFieldUpdater<AbstractReferenceCounted> AIF_UPDATER =
      AtomicIntegerFieldUpdater.newUpdater(AbstractReferenceCounted.class, "refCnt");

  private static final ReferenceCountedUpdater<AbstractReferenceCounted> updater =
      new ReferenceCountedUpdater<AbstractReferenceCounted>() {
        @Override
        protected AtomicIntegerFieldUpdater<AbstractReferenceCounted> updater() {
          return AIF_UPDATER;
        }

        @Override
        protected long unsafeOffset() {
          return REFCNT_FIELD_OFFSET;
        }
      };

  // Value might not equal "real" reference count, all access should be via the updater
  @SuppressWarnings("unused")
  private volatile int refCnt = updater.initialValue();

  boolean isAccessible() {
    // Try to do non-volatile read for performance as the ensureAccessible() is racy anyway and only
    // provide
    // a best-effort guard.
    return updater.isLiveNonVolatile(this);
  }

  @Override
  public int refCnt() {
    return updater.refCnt(this);
  }

  /**
   * An unsafe operation intended for use by a subclass that sets the reference count of the buffer
   * directly
   */
  protected final void setRefCnt(int refCnt) {
    updater.setRefCnt(this, refCnt);
  }

  /**
   * An unsafe operation intended for use by a subclass that resets the reference count of the
   * buffer to 1
   */
  protected final void resetRefCnt() {
    updater.resetRefCnt(this);
  }

  @Override
  public ReferenceCounted retain() {
    return updater.retain(this);
  }

  @Override
  public ReferenceCounted retain(int increment) {
    return updater.retain(this, increment);
  }

  @Override
  public boolean release() {
    return handleRelease(updater.release(this));
  }

  @Override
  public boolean release(int decrement) {
    return handleRelease(updater.release(this, decrement));
  }

  private boolean handleRelease(boolean result) {
    if (result) {
      deallocate();
    }
    return result;
  }

  /** Called once {@link #refCnt()} is equals 0. */
  protected abstract void deallocate();
}
